(1) Field of the Invention
The present invention relates to a magnet roll, more specifically a magnet roll comprising bonded magnet blocks and a shaft of a polygonal cross section. It also relates to a method of producing such a magnet roll.
(2) Description of the Prior Art
A magnet roll device comprising a permanent magnet roll having a plurality of magnet poles and a cylindrical nonmagnetic sleeve surrounding the magnet roll in a rotatable relationship to each other is used for conveying powdery developers in magnetic brush developing, magnetic brush cleaning, etc.
Magnet rolls of various structures have been proposed, and some of them comprise permanent magnet blocks instead of integral, cylindrical magnets. Permanent magnet blocks are advantageous over integral, cylindrical magnets in that the former can provide a magnet roll with a lot of magnet poles more easily than the latter. Further, permanent magnet blocks made of magnet powder and plastics are advantageous over sintered blocks in that the former has somewhat flexibility which is needed for assembling and bonding the blocks which inevitably have dimensional irregularities such as warps.
Various magnet rolls comprising anisotropic bonded magnet blocks secured onto a shaft have been disclosed. See U.S. Pat. No. 3,455,276. This patent discloses a magnet roll comprising a plurality of fan-shaped magnet blocks bonded to a central, round shaft and also to each other. These magnet blocks, however, are not provided with any means for ensuring the precise positioning thereof. Also, since the magnet blocks have the same shape, complicated magnet pole arrangements cannot be attained.
Thus, although magnetic blocks are very convenient to provide a magnet roll with lots of magnet poles which may be different from each other in strength and direction of magnetization, they encounter difficulties in being precisely positioned onto a shaft.